1. Field of the Invention
The present invention relates to a hologram recoding method, a hologram reproduction apparatus, a hologram reproduction method using the same and a flat display element apparatus, and more particularly, to a hologram recording method using a beam with a very large incident angle, a hologram reproduction apparatus using a holographic reflector, a hologram reproduction method using the same and a flat display element apparatus using a holographic reflector.
2. Description of the Related Art
A hologram refers to a three dimensional (3D) photographic image photograph created by means of a holography through a laser beam, which is produced in a such a fashion that a reference beam or one beam of two laser beams into which is divided by a beam splitter, and an object beam or the other divided by the beam splitter and then directed to and diffused from an object of interest to be recorded as information are projected onto a recording medium to record, in a photographic form, a large number of minute inference fringes produced by the interaction of the reference beam and the object beam on the surface of the recording medium so as to form an image of the original object.
Dennis Garbor has originally invented a hologram in 1948. From that time up to now, most widely used types of holograms include a two-beam transmission hologram developed by E. Leith et al., an one-beam reflection hologram developed by Denisyuk et al., and an edge-lit hologram developed by N. Phillips et al., and the like.
For such a transmission hologram, in the recording of it, all the reference and object beams are projected onto a recording medium in the same direction with respect to the recording medium to produce a hologram, and in the reproduction of it, a reference beam with same wavelength as that of the reference beam projected in the recording of the hologram illuminates the surface of the recording medium on which the hologram has been recorded, at the same incident angle as that in the recording of the hologram, while passing through the recording medium to obtain a reproduction beam to reconstruct the hologram in a direction opposite to the incident direction of the reference beam through diffraction and diffusion of the reproduction beam due to the interference fringes so as to form an image of the original object. At this point, the reproduction of the hologram means that information recorded on the hologram is represented visually.
For such a reflection hologram, in the recording of it, the reference beam and the object beam are projected onto the recording medium in the direction opposite to each other, in the reproduction of it, a reference beam with same wavelength as that of the reference beam in the recording of the hologram illuminates the surface of the recording medium on which the hologram has been recorded, at the same incident angle as that in the recording of the hologram, while being reflected by the recording medium to obtain a reproduction beam to reconstruct the hologram in the same direction as the incident direction of the reference beam so as to form an image of the original object.
FIG. 1 is a schematic view illustrating a general transmission type hologram recording method according to the prior art.
As shown in FIG. 1, a reference beam 11 and an object beam 13 are simultaneously projected onto a recording medium 15 in such a fashion that they are identical with each other in their incident directions.
FIG. 2 is a schematic view illustrating a general reflection type hologram recording method according to the prior art.
As shown in FIG. 2, a reference beam 11 and an object beam 13 are simultaneously projected onto a recording medium 15 in such a fashion that they are opposite to each other in their incident directions. In order to obtain a maximum efficiency in the recording of the hologram, the incident angles of both the reference and the object beams must be maintained at a predetermined angle. For this reason, an incident angle of a reference beam in the reproduction of the hologram must also be maintained at the predetermined angle to be identical with that of the reference beam in the recording of the hologram.
FIG. 3 is a schematic view illustrating a general transmission type hologram reproduction method according to the prior art.
As shown in FIG. 3, a reference beam 11 with the same wavelength and incident angle as those of the reference beam in the recording of the hologram illuminates the surface of the recording medium on which the hologram 17 has been recorded while passing through the recording medium to obtain a reproduction beam to reconstruct the hologram 17 in a direction opposite to the incident direction of the reference beam through diffraction and diffusion of the reproduction beam due to the interference fringes so as to form an image of the original object.
FIG. 4 is a schematic view illustrating a general reflection type hologram reproduction method according to the prior art.
As shown in FIG. 4, a reference beam 11 with the same wavelength and incident angle as those of the reference beam in the recording of the hologram illuminates the surface of the recording medium on which the hologram 17 has been recorded, at the same position as that in the recording of the hologram, while being reflected from the recording medium to obtain a reproduction beam to reconstruct the hologram 17 in the same direction as the incident direction of the reference beam so as to form an image of the original object.
FIG. 5 is a schematic view illustrating a color separation due to a diffraction of a reference beam generated in the reproduction of a transmission type hologram according to the prior art. A reproduction beam 19 formed by allowing the reference beam 11 to pass through or reflected by the recording medium on which the hologram 17 is recorded reproduces information recorded on the hologram 17, which makes it possible for an observer to view it in a stereoscopic or planar form.
In case of reproduction of a hologram based on such conventional hologram recording methods, a light source must be provided separately and the same condition as that in the recording of the hologram must be prepared. Accordingly, the conventional hologram reproduction methods are accompanied by the restraints on a place where the reproduction of the hologram is implemented. Also, in case of a holographic optical element (hereinafter, referred to as “HOE”), the size of an entire system becomes larger. Particularly, since the condition of irradiation for the reference beam at the time of reproducing a transmission type hologram must be identical with that of irradiation for the reference beam at the time of recording it, there may occur a problem in the place where a hologram is reproduced or the structure of a hologram reproduction apparatus.
In particular, as shown in FIG. 5, in the case where the hologram 17 or HOE has been recorded on a recording medium, and then is reproduced in a full color image form, a reproduction beam 19 is separated depending on its wavelength according to an irradiation angle of the reference beam 11.
In order to resolve this problem, in the recording of the hologram, a mirror is often used. But, this approach has a disadvantage in that it is not easy to adjust an angle of reflection of the mirror. Also, in case of employing other gratings or HOE, there occurs a color separation according to wavelengths of light beams, and the characteristics of a noise are insufficient. In particular, in case of producing a hologram in a full color image form, efficiency is degraded.
In addition, for a conventional edge-lit hologram, it is very complicated to record a hologram and efficiency is degraded.
In general, it has been known that when a full color hologram or HOE is recorded on one recording medium, efficiency is lowered to ½, and reliability of color reproduction is decreased.
Further, it is difficult to adjust a hologram reproduction angle (reflection angle) by color.